Time switch mechanisms have been proposed in which a heated bimetallic member activates a mechanical ratchet which, after heating the bimetallic member, releases a component under spring tension which advances one step. Thus, several heating cycles and cooling cycles of the bimetallic member may be connected in succession, to prolong the switching time in relation to the mere single heating of the bimetallic member. However, with these time switch mechanisms, the switching time can only be adjusted in steps and the mechanism is also relatively expensive and, like all mechanisms, is liable to break down and is exposed to wear.